1. Field of the Invention
The invention relates to a method of producing three-dimensional bodies which wholly or for selected parts consist of amorphous metal.
2. Description of the Related Art
When cooling a metallic material from melt to solid phase, a polycrystalline structure is usually provided. Here the microstructure consists of a large number of different grains, the atoms in each grain being arranged according to some kind of regular pattern. The number of grains and the size of the grains can be affected, for example by using different cooling speeds from melt or by different types of mechanical working and heat treatment of the solid material. If the entire material consists of one crystal, a single crystal material is obtained, in which all atoms are positioned in a mutually ordered manner. If the atoms are instead completely disordered and there are no grains with regularly positioned atoms, the material is said to be amorphous. This can be achieved, for example, by cooling a melt very rapidly so that there is no time for grains to grow, or by very extensive mechanical deformation where the grains are disrupted. Generally seen materials with amorphous structure are common. For example, many polymer materials are wholly or partly amorphous in solid phase since the relatively complex molecule makes crystallisation to repeatable units difficult. There are also many metal oxides which easily form an amorphous structure. At the beginning of the sixties, the first amorphous metals were produced by a thin layer of melt being sprayed on a heat-conducting base. This resulted in very high cooling speeds of 105-106 K/s and there was no time for grains to grow, but the disordered structure was maintained also in the solid phase. The resulting alloys, however, were very thin with a thickness of just some tenths of a micrometer and therefore had limited ranges of application.
Amorphous bulk metals or amorphous structural metals, that is amorphous metals with dimensions that permitted structural applications, were not produced until the seventies from specially composed alloys. Bulk metals of these alloys were produced by cooling from melt at a cooling speed of about 1000 K/s but contained, inter alia, the expensive metal palladium, which prevented large volumes of production. At the end of the eighties Professor Inoue at the Tohoku University in Japan managed to develop various multicomponent systems consisting of common metallic elements which resulted in an amorphous bulk structure when cooling from melt. In the years that followed a great number of different amorphous metal systems have been found.
Table 1 below exemplifies some amorphous metal systems and the maximum thickness in which they can presently be cast and the critical cooling speed for an amorphous bulk structure to be formed.
MaximumCritical coolingAlloy systemthickness mmspeed K/sLantanide-Al—(Cu,Ni)10200Mg-Lantanide-(Cu,Ni)10200Zr—Al—(Cu,Ni)30 1-10Zr—Ti—Al—(Cu,Ni)301-5Zr—Ti—(Cu,Ni)—Be301-5Fe—(Al,Ga)—(P,C,B,Si,)3400Pd—Cu—Ni—P750.1Fe—(Co,Ni)—(Zr,Hf,Nb)—B6200
The greatest problem in casting of three-dimensional bodies (bulk metal) of amorphous metal is to achieve a sufficient cooling speed. An insufficient cooling speed results in a crystalline material instead of an amorphous material. The cooling speed restricts the size and thickness of material to be produced. The required cooling speed also makes it difficult to cast complicated geometries, thus making it necessary to produce several different components to be assembled. In practice, there will only be a limited choice of materials since there is a limited number of alloy systems that have a critical cooling speed that is practicably handleable in casting of construction components.